Metal-casting mold



' Aus-25, 1925. 1,550,957..-

A. T. GRAHAM METAL CASTING MOLD Filed Feb. l2, 1923 Y UNITED STATES ARTHUR T. GRAHAM, OF SAN FRANCISCO, CALIFORNIA.

PATENT OFFICE.

METAL-CASTING MOLD.

Application filed February 12, 1923. Serial No. 618,647.

To all whom t may concern:

Be it known that I, ARTHUR T. GRAHAM, a citizen of the United States, residing at San Francisco, in the county of San Francisco, State of California, have invented a new and useful Metal-Casting Mold, of which the following is a specilication in such full and clear terms as will enable those skilled in the art to construct and use the same'.

This invention relates to a metal casting mold, and its object is to produce sharp castings regardless of the fact that most metals contract slightly at the point of solidiication.

It will be understood by those skilled in the art that nearly all metals, except anti- Inony, expand considerably upon heating and contract slightly at a more than normal rate of expansion at the point of solidification. This makes it necessary to produce nearly all molds of a size slightly larger than the size the final casting is to be. This disadvantage does not make any great difference where the casting is to be machined toa given size,but in the case of dental work, where it is necessary to produce sharp castings and to use them practically without machining, it is a great disadvantage and necessitates some method of producing castings which will result in a casting as nearly the proper size as it is possible to get it. `With the present invention the mold is lled with metallic particles having substantially the same coefcient of expansion Lunder heating as the metal to be cast.

crete is made is ordinarily, in dental work, a kind of plaster, but in other classes of work it may be simplymsai l orwother fine metalala Whiehlels'l tileslllntal, as indicated at 3, are'bedded, said particles beiig large enough in number to substantially lill the mold with the sand and plaster particles, simply lilling the voids between the larger particles.

As a result of the foregoing method o-f producing the mold, the coeiiicient of expansion of the mold is determined by the large number of metal particles contained in it, and which particles are substantially in Contact with each other, or at least, sufficiently near in Contact with each other to expand the mold at substantially the same rate of expansion as the metal to be cast, whereby the opening in the mold is increased in size, and as the mold cools olf, it is reduced in size to its original condition thereby, nearly yas may be, producing a sharp casting.

In order to prevent the metal particles in the body of the mold from amalgamating with the heated metal to be cast, the metal particles are made of a material which will melt at a slightly higher degree of temperature; than the metal casting, and the inside of the mold is coated with a lireproof paint, as indicated at 4C, to prevent the metal to be cast from adhering to the mold.

It will be understood by those skilled in the art that the shape of the metal particles is immaterial, the only thing requisite being that they be suiiicient in number to give to the mold substantially the same coeficient of expansion under heat as the metal to be cast will have, and that the matrix be sufficient in quantity to hold the mold together properly and capable of withstanding substantially the same high degree of heat as is required to melt the metal for the casting.

What I claim is as follows, but modifications may be made in carrying out the invention shown in the drawings as particularly described within the purview of the disclosures :l

l. A metal `casting mold comprising a mold made up of granular particles in sufticles of substantially the same eoeflicient cient number of such a material as to give of expansion as the metal to be east and the mold substantially the same ooeioient a binder for holding said particles together. 10 of expansion and contraction as the metal In testimony whereof I have hereunto 5 to be east. set my hand. this day of February 2. A metal casting mold comprising a A111923. mold made up of a body of granular par- ARTHUR T. GRAHAM.

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